Add a feature guard for test function relying on networkproxy.
Pick-to: 6.8
Task-number: QTBUG-136101
Change-Id: I69d97c84fb7d68f33f4b74fc8fd6665b1b8d6717
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
(cherry picked from commit 11b54b85ce74d59173afd297b780d3170b331548)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>